Technique for manufacturing micro-electro mechanical structures

Abstract

A technique for manufacturing a micro-electro mechanical structure includes a number of steps. Initially, a cavity is formed into a first side of a handling wafer, with a sidewall of the cavity forming a first angle greater than about 54.7 degrees with respect to a first side of the handling wafer at an opening of the cavity. Then, a bulk etch is performed on the first side of the handling wafer to modify the sidewall of the cavity to a second angle greater than about 90 degrees, with respect to the first side of the handling wafer at the opening of the cavity. Next, a second side of a second wafer is bonded to the first side of the handling wafer.

Description

TECHNICAL FIELD [0001]The present invention is generally directed to a micro-electro mechanical structure and, more specifically, to a technique for manufacturing micro-electro mechanical structures.BACKGROUND OF THE INVENTION [0002]A variety of techniques have been utilized to manufacture micro-electro mechanical (MEM) structures, which are now utilized in a variety of applications to perform a number of functions. For example, MEM structures have been utilized in pressure sensors that are currently employed in many automotive and consumer products. A common technique for manufacturing silicon pressure sensors has involved forming sense elements on top of a silicon wafer and wet etching through a back side of the wafer (to an etch stop layer) to create a thin silicon membrane, under the sense elements. The sense elements, e.g., piezoresistive or capacitive elements, are implemented to sense a deflection of the membrane. In a typical process, the wet etch leaves a 125.3 degree angle...

AI Technical Summary

Benefits of technology

The present invention is about a technique for making micro-electro mechanical (MEM) structures. The technique involves forming a cavity in a handling wafer, adjusting the sidewall of the cavity to a second angle greater than about 54.7 degrees, and bonding a second wafer to the first wafer. The second wafer may be an epitaxial wafer with a buried etch stop layer. The technique can be used to create thin membranes with a thickness between about 10 microns and 25 microns. The first and second wafers may be N-type silicon wafers with specific Miller Indices. The invention also includes a hole formed through the handling wafer to create a differential pressure sensor.

Problems solved by technology

While this technique has proven relatively successful, the area of the sensor has been larger than electrically necessary, due to the constraints imposed by the wet etch, which follows the crystalline planes of the silicon and typically provides a membrane having a diameter of about 500–1500 microns.

While an anisotropic dry backside etch could be utilized to etch all of the crystalline planes equally and, thereby, reduce sensor area, there are currently no reliable etch stops that adequately maintain membrane thickness for current dry etch processes.

As such, sensors made with this process have a less robust membrane, as the membrane is not as well supported as a sensor made with the backside cavity process.

Furthermore, while the cavity-on-top version of the sensor has been successfully used to create absolute pressure sensors, the lack of an etch stop on the underside of the membrane makes it difficult to create differential pressure sensors using the cavity-on-top process.

Unfortunately, stress control of thin film membranes is generally inferior to stress control of single-crystal silicon membranes.

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